This invention relates to a mountaineering back pack and, more particularly, to an improved frame assembly for such a pack which is adapted for limited flexing.
Most back pack frame assemblies of the prior art have included frames having a pair of spaced vertical side bars and a plurality of cross bars extending between them in spaced parallel relation. The side bars and cross bars are bolted, fused or clamped together to form relatively rigid structures. Nylon or canvas bags are then typically secured to the frame assembly for holding at least portions of the load.
This type of frame assembly is in turn supported on the hiker's back by a pair of shoulder straps and also by a hip belt that is cinched tightly around the hiker in the region of the hips. Considerable effort has been directed in recent years toward the design of back packs that are capable of being supported primarily on the hips. It has been determined that such an arrangement is desirable in order to maximize load carrying ability and comfort.
In walking, the hips of the hiker rotate fore and aft about a vertical axis extending generally through the torso. There is also some control-rotational shoulder movement about the same axis, but to a much lesser extent. It is desirable from the load carrying and comfort standpoints that the frame assembly remain in generally parallel relation with the plane of the back during such body movement and closely adjacent thereto, yet not inhibit the relatively free fore and aft rotational movement of the hips.
In an effort to achieve these desired ends, some packs in the past have equipped relatively rigid pack frames with various types of specially designed pivotal and flexible couplings between the pack frames and the hip belt assemblies. These devices have suffered from various deficiencies. In some instances, they simply do not serve to avoid undue restriction of the hips. One approach that does reduce restriction involves providing a universal joint type coupling allowing for relatively free movement between the frame and hip belt assembly. However, this results in a shifting or swaying of the frame and supported load as the hiker walks, producing a generally unstable feeling. Efforts to avoid this instability have been towards the design of generally complicated and inherently expensive devices.
In prior devices which have frame members welded or screwed together, there is some tendency to weaken the structure at the joint. Problems have been minimized by resort to high strength or to heavier materials or to complex joints that rigidly lock the mating parts together. However, these expedients undesirably add to the cost or make the frame heavier, or both. Moreover, all such constructions, in effect, have fulcrum points at the joints about which destructive bending can occur. Further, such constructions are not particularly well suited for absorbing shock loads such as occur when the pack is dropped.
It will be appreciated from the foregoing that there is a need for a back pack frame that is strong and durable, yet simple, lightweight and relatively inexpensive to build and that allows the shoulders and hips to rotate relatively freely and independently, without resulting instability. The present invention fulfills this need.